1. Field of the Invention
The present invention relates to lifting apparatus for mounting on a support structure and particularly for mounting on a motor vehicle such as a flatbed truck to form a lifting-transporting vehicle. One of its main uses is in lifting one end of another vehicle and moving the latter to another location, i.e. to perform much the same function as a convention tow-truck, but in an improved manner. It can also be used to lift, and in some cases, to transport other large objects such as motors of vehicles and large garbage bins.
2. Description of the Prior Art
The lifting apparatus of a conventional tow truck includes one or more chains which are connected to the bumper or axle of a vehicle to be towed. The chain is then taken up by a winch assembly to bring the bumper of the vehicle firmly against one or more flexible straps. This causes the chains and/or the straps to bear against the lower portions of the bumper and/or underlying body portions of the vehicle as they curve around and under the end of the vehicle with a force equal to the weight being lifted. This almost inevitably causes damage to these parts of the vehicle. As the vehicle is being towed, it thrashes about on the chains and straps causing additional damage.
Several attempts have been made to improve on this conventional type of lifting apparatus for tow trucks. For example, U.S. Pat. No. 3,285,443 discloses a lifting and towing device in which the usual chains are replaced by a rigid structure which engages only the axle of the vehicle to be towed so that there is no bearing against the bumper and underlying body portions of the car. The device employs a parallelogram type linkage to maintain the rigid lifting members in substantially horizontal disposition as they are raised. The device suffers from several disadvantages. The parallelogram linkage is attached to the very end of the bed of the tow truck and extends outwardly therefrom. It is, of necessity, relatively small, delicate, and mechanically complicated. It does not have sufficient structural strength or stability to be directly lifted by the elevating means, and a separate boom must be provided. Finally, the device is only capable of raising and towing a vehicle and is not readily adaptable for other modes of operation. A similar device is shown in U.S. Pat. No. 3,051,337.